"Yes," was the reply, "the progress in the last half of the nineteenth century has been greater than in the preceding twenty centuries. From the days of Herodotus--two thousand years ago--till within the present generation exploration of the valley of the Nile had accomplished very little. Syene, at the first Cataract of the Nile, was a city in the days of the ancient dynasties of Egypt; three thousand years ago the kingdoms of Ethiopia flourished, and their rulers had a prominent place in history. Time and time again men sought in vain to solve the mystery of the source of the Nile, and it was reserved for men of our day to make the great discovery." One of the boys asked to whom the honor belonged of ascertaining the source of the Nile. "That question is a conundrum," replied the Doctor, with a smile, "and a conundrum that needs an explanation before answering. The honor belongs to several explorers, and not to one alone. Each has made discoveries peculiarly his own, and these discoveries have supplemented the work of the rest. "As I have before told you, it was long supposed that the Blue Nile was the parent stream, and its sources were ascertained by James Bruce. The error of this belief was set forth after the death of Bruce, as the White Nile was found to be of greater volume than the Blue, and was explored to a point more distant from the junction of the two streams than were the springs of the Blue Nile. Mohammed Ali sent three expeditions to find the sources of the White Nile, but they failed in their efforts. Private expeditions were sent every few years, but with the same results. The heat, the fevers, the hostility of the natives, the difficulty of penetrating marshes and tropical forests, all conspired to frustrate their efforts. The first expedition of Mohammed Ali reached latitude 6° 30' north; the second went to 4° 42' north; and the third stopped at about 5° north. Dr. Knoblecher, in 1849, went to 4° 10' north, which was farther than any one else had gone. Miani, an Italian traveller, went to a point about 3° 32' north, and about the same time Dr. Schweinfurth explored the Bahr-el-Gazal, one of the tributaries of the White Nile, in the expectation that it might turn out to be the main stream. Miss Tinné, a Dutch lady, also explored that river, and spent more than a year in its valley." "What!" exclaimed one of the youths, "a lady going on an expedition in Africa! She must have been fond of adventure. Who was she?"